An antenna array is a group of multiple active antennas coupled to a common source or load to produce a directive radiation pattern. Usually, the spatial relationship of the individual antennas also contributes to the directivity of the antenna array. A phased array antenna is an array of antennas in which the relative phases of the signals feeding the antennas are varied in a manner that the effective radiation pattern of the entire array is reinforced in a desired direction and suppressed in undesired directions.
FIG. 1 shows a diagram of a conventional antenna array 100. The antenna array 100 includes several linear arrays 104 housed in a (non-metallic) radome 102. Here, each linear array 104 is arranged vertically with spacing between each other, which is determined by the desired resonant frequency of the antenna array 100. Each linear array 102 is connected to its associated radio frequency (RF) electronics circuitry contained in an external RF electronics module 108, via an antenna feed 106. The RF electronics module 108 is connected to external systems via a connection 110 for power, control, and communications connections; and may be physically mounted on the radome 102, or may be located remotely or outside of the antenna array 100.
An Electronically Scanned Array (ESA) is a type of phased array antenna, in which transceivers include a large number of solid-state transmit/receive modules. In ESAs, an electromagnetic beam is emitted by broadcasting radio frequency energy that interferes constructively at certain angles in front of the antenna. An active electronically scanned array (AESA) is a type of phased array radar whose transmitter and receiver (transceiver) functions are composed of numerous small solid-state transmit/receive modules (TRMs). AESA radars aim their beam by emitting separate radio waves from each module that interfere constructively at certain angles in front of the antenna.
Digital beamforming is a signal processing technique used in sensor or radar arrays for directional signal transmission or reception. Digital beamforming is attained by combining elements in a phased array in such a way that signals at particular angles experience constructive interference, while other signals experience destructive interference. Digital beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. An advantage of digital beamforming is transmitting multiple simultaneous summed signals through each radar element.
Modern radar, radar jammer and communications antenna systems often require wideband frequency capability within constrained volume allocations. Electronically Scanned Array (ESA) antenna and Active Electronically Scanned Array (AESA) antenna designs provide dense-packed, high-reliability electronics.
There are growing interests to use digital beamforming to transmit two or more different types of signals simultaneously such as communications (comms) signals, commercially available Long-Term Evolution (LTE) protocol signals, radar signals, and/or electronic warfare (EW) signals. This requires spectrum sharing by the different types of signals, for example, a radio frequency (RF) signal for military or radar applications, and a lower frequency (communication) signal for command and control applications, need to be simultaneously transmitted off a radar array.
For example, military radars and unmanned aircraft systems (UAS) that provide EW function may require concurrent use of C2 data links, the quality of service of which is not adversely effected by the RF fratricidal affects from EW and/or radar signals.
However, many conventional methods require separate, custom systems for each type of application/mission. Moreover, in the conventional systems, high peak-to-average power ratio (PAPR) for OFDM waveforms becomes a problem for the amplification stages for radar system.
Also, interleaving OFDM subcarriers dedicated for radar systems among communication subcarriers modulated with message symbols increase Integrated Side Lobes ratios and thus reducing SAR contrast image quality. Additionally, proposed optimal schemes are computationally expensive and have poor to moderate data rates.
As a result, there is a need for a method and system to allocate spectrum for a variety of commercial communication protocols, such as LTE protocol, in a radar-prioritized modes, and to perform radar modes within commercial communication protocols accurately and effectively.